Various power conversion systems have been used over the years. Among such power conversion systems, converters are used to convert DC (direct current) to DC, whereas inverters are used for converting DC to AC (alternating current). Radio frequency power amplifiers perform high frequency power conversion by using a RF (radio frequency) input and a DC input to provide a RF output with a significantly higher power than the RF input.
In order to reduce the size of such power converters, power conversion frequencies have been pushed into the MHz range. The size reduction is primarily due to the smaller size of passive magnetic components as the frequency is increased. Currently, the power densities are of the order of 50-100 Watts/in.sup.3. Further improvement power densities (&gt;200 Watts/in.sup.3) is required for the upcoming high performance electronic systems such as massively parallel supercomputers. For higher power densities, it is advisable to consider frequencies in 10-1000 MHz range. The circuit topologies for such high frequency power conversion are of the resonant type. The resonant inductor used in such designs is the most critical passive component. Specifically, high circulating currents greatly stress the inductor. Thus the inductor requires a very high quality factor, of the order of 1000.
It has been difficult, if not impossible, to fabricate an inductor having the necessary characteristics for such high frequency power conversion applications using normal metallic conductors such as copper. Specifically, the skin effect causes currents to flow essentially at the surface of conductors at higher frequencies. The relatively high surface resistance of normal conductive metals such as copper tends to reduce the Q of the inductor. As the frequency gets higher, the current is even more concentrated at the surface corresponding effectively to a reduction in the cross-sectional area through which the current may flow such that the resistance is increased further.